Basically, a glass bulb for a cathode-ray tube used in manufacturing a color television set, a computer monitor or the like includes three components, i.e., a panel on which an image is projected, a conic funnel engaged to a rear surface of the panel, and a tube-shape neck adhered to an apex of the funnel. The panel, the funnel and the neck are all made of glass. Especially, the panel and the funnel are manufactured by press-molding a molten glass lump called a gob into a desired size and shape.
Further, the panel has a face and a skirt. Fluorescent materials for forming an image are coated on an inner surface of the face and a shadow mask having a plurality of holes is supported with pins on the skirt. Furthermore, an electron gun and a deflection yoke are installed at an inner and an outer side of the neck, respectively, wherein the electron gun forms an image by firing an electron beam toward the fluorescent materials through the holes of the shadow mask.
Such a cathode-ray tube is installed in a cabinet included as an external portion of the color television set or the computer monitor. However, since the face of the panel is positioned inside the cabinet and is seen through the window of the cabinet, an edge portion of the face of the panel may not be seen due to a width of the window frame of the cabinet depending on the position of a viewer, thereby reducing viewing area.
In Korean Patent Laid-Open Publication No. 2000-73436, there is disclosed an art capable of preventing the reduction of the viewing area by forming a recessed fitting portion along the edge of the face of the panel within a width range as to not interfere with the useful screen area and arranging the fitting portion of the panel flat on the window of the cabinet.
Since, however, the aforementioned prior art merely proposes that the fitting portion be formed at the face of the panel, without due regard to be paid to characteristics of a cathode-ray tube, there can occur various technical problems in practically applying the prior art to the manufacture of the panel. That is, in manufacturing the panel for the cathode-ray tube, implosion-proof characteristics of UL (underwriters' laboratories) standards should be satisfied, for example. Especially, in case that inside of the glass bulb becomes vacuum by evacuating the air therefrom, due to an atmospheric pressure difference between the inside and the outside of the glass bulb, a compressive stress will be generated on an inner surface of the glass bulb and a tensile stress on an outer surface of the glass bulb. In this case, a blend round portion connecting the face of the panel to the skirt thereof is subject to a maximum vacuum tensile stress due to the aforementioned atmospheric pressure difference, and therefore it is structurally very weak against a breakage or an implosion. Accordingly, the distribution of the vacuum tensile stress and the mechanical strength should be properly taken into account in designing and manufacturing the recessed fitting portion in the face of the panel.